Properties of organic electronic materials such as low cost and high flexibility have made outstanding progress as compared with those of related art semiconductor materials. In particular, organic bistable materials in which switching phenomenon is observed when voltage is applied to the materials until the voltage reaches or exceeds a certain value and current in a circuit suddenly increases, have been examined their application to high-density organic memory elements or the like.
The operating mechanism of such elements is attained by reversible switching between two resistance states. For example, Yang Yang et al. has shown a nonvolatile memory produced by forming a thin film of a high conductivity material such as aluminum, copper, silver, gold, nickel, magnesium, indium, calcium, and lithium, or by dispersing the high conductivity material as fine particles in an organic semiconductor such as aminoimidazole dicarbonitrile (AIDCN) and hydroxyquinoline aluminum (Alq), and an organic insulator such as polystyrene and PMMA. With this structure, the nonvolatile memory can achieve the bistability of a high resistance state and a low resistance state by applying voltage, and retains information even if the voltage is zero (see Patent Documents 1 and 2, and Non-patent Document 1).
In addition, Patent Document 3 discloses a switching element in which platinum or rhodium fine particles having an average particle diameter of 5 nm or less are dispersed as conductive fine particles in an organic bistable material layer having an electron donating functional group and an electron accepting functional group in one molecule thereof. With this structure, fine particles having little variation in particle diameter can be dispersed uniformly in a fine particle dispersion layer having thin film thickness, so that a switching element having stable properties can be obtained.    Patent Document 1: Japanese Translation of PCT International Application No. JP-A-2004-513513    Patent Document 2: Japanese Patent Application Publication No. JP-A-2005-101594    Patent Document 3: Japanese Patent Application Publication No. JP-A-2004-200569    Non-patent Document 1: Proceedings of the IEEE, 93, 7 (2005)